Move context-related callbacks into OutputSurface

cc/output/output_surface.h

Index: cc/output/output_surface.h
diff --git a/cc/output/output_surface.h b/cc/output/output_surface.h
index 2e7a190c6a51a73327cec0493a06a1dc8f851e90..8ebf01c3c728bb13de9d784b1c6f084477f8edb0 100644
--- a/cc/output/output_surface.h
+++ b/cc/output/output_surface.h
@@ -20,6 +20,7 @@ namespace cc {
 
 class CompositorFrame;
 class OutputSurfaceClient;
+class OutputSurfaceCallbacks;
 struct LatencyInfo;
 
 // Represents the output surface for a compositor. The compositor owns
@@ -102,6 +103,8 @@ class CC_EXPORT OutputSurface {
   scoped_ptr<cc::SoftwareOutputDevice> software_device_;
   bool has_gl_discard_backbuffer_;
 
+  scoped_ptr<OutputSurfaceCallbacks> callbacks_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(OutputSurface);
 };